I would say there is almost "never" the case where changing a bus route into a tram route say a fall of public transport users. Indeed, the point of going for a tram or light rail is that it is seen as of being of a higher quality and is able to attract people from their cars. Even dreadful old bigots like you.
How is it higher quality when you have less chance of getting a seat than you did when the service ran with buses? The fastest transport on the route will still be the airport bus as it's a limited stop service (it didn't cost £500M - and climbing day by day).........